The velocity factor VF of electromagnetic waves in the transverse electric and magnetic, TEM, mode in ordinary transmission lines with the field immersed in a uniform dielectric of relative permittivity εr, relative to air, is VF=1/√εr.
Therefore, the relative phase between the input and output of a fixed length of transmission line may be varied by changing either the effective relative permittivity of the surrounding material, or the amount of the line surrounded by a dielectric relative the amount of the line surrounded by air.
A TEM transmission line is characterized by its characteristic impedance Z and its phase velocity v. These two parameters are given by the capacitance C and inductance L per unit length:
      Z    =                  L        C                  v    =          1      /                        L          ·          C                    
The capacitance is proportional to the relative permittivity εr of the transmission line and both the capacitance and inductance depend on the cross-section of the line. In particular, the inductance will increase with the separation between the conductors. Ordinary electrical cables cannot be used to carry currents in the radio frequency range or higher, which reverse direction millions to billions of times per second, because the energy tends to radiate off the cable as radio waves, causing power losses. Radio frequency currents also tend to reflect from discontinuities in the cable such as connectors and joints, and travel back down the cable toward the source. These reflections act as bottlenecks, preventing the signal power from reaching the destination. Transmission lines use specialized construction, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. The distinguishing feature of most transmission lines is that they have uniform cross sectional dimensions along their length, giving them a uniform impedance, called the characteristic impedance, to prevent reflections. Types of transmission line include parallel line (ladder line, twisted pair), coaxial cable, stripline, and microstrip. The higher the frequency of electromagnetic waves moving through a given cable or medium, the shorter the wavelength of the waves. Transmission lines become necessary when the length of the cable is longer than a significant fraction of the transmitted frequency's wavelength.
In the phase shifters using moving dielectrics as described in prior art, the impedance of the transmission line varies with the movement of the dielectric. This may be a problem.
U.S. Pat. No. 3,005,169, “Fye”, 1961, discloses a microwave phase shifter aiming at overcome some of these problems. However, Fye e.g. does not disclose how a connection can be achieved between the disclosed “outer plates” and proper ground.